We had the basic "Baby Weavers" one from Kiddicare.com. Seemed really sturdy - but was quite bulky and heavy. Can't have it both ways, I guess! We (occasionally) used it as a "Time Out" area for DD when she was throwing a major tantrum and it never budged an inch! I think they cost about £30-£35.

we have a baby dan one that is great (it is extra long) but again it's quite heavy.

Why not pick one up second hand? I'm planning on selling ours soon but it would be too heavy to post, there is a good second hand market though and travel cots are often on gumtree and the like having had very little use.